EP1612200A2

EP1612200A2 - Fertilising composition and process for the obtainment thereof

Info

Publication number: EP1612200A2
Application number: EP05380062A
Authority: EP
Inventors: Jose Maria Garcia-Mina Freire
Original assignee: Inabonos SA
Current assignee: TIMAC AGRO ESPANA SA
Priority date: 2004-06-28
Filing date: 2005-04-05
Publication date: 2006-01-04
Anticipated expiration: 2025-04-05
Also published as: PL1612200T3; DK1612200T3; EP1612200B1; EP1612200A3; PT1612200E; SI1612200T1; ES2245605B1; ES2245605A1

Abstract

A fertilising composition comprising an inorganic matrix insoluble in water but soluble in the organic acids released by the plant roots into the rhizosphere, wherein said matrix comprises in turn one or several double salts of phosphorus with calcium or magnesium, and one of the metals chosen from Fe, Al, Mn, Cu, Zn, B and Co, with the condition that the Al is chosen only when the other element of the double salt is Mg, and wherein the double salts are optionally chemically associated to organic compounds with chelating ability by means of metal bridges. The composition may further contain an initiating fraction formed by soluble salts of Fe, Al, Mn, Cu, Zn, B and Co, and one or several components chosen from nitrogen and potassium sources, organic matter sources, nitrification or urea hydrolysis inhibitors, phytoregulators and pesticides may optionally be incorporated thereto; a method for preparing the fertilising composition and a method for fertilising the soil are also provided.

Description

FIELD OF THE INVENTION

The present invention relates to a fertiliser with high bioacceptance and a low degree of leaching or washout, the nutrient release of which is controlled by the plant by means of the organic acids it releases to the rhizosphere, and a process for the preparation thereof.

BACKGROUND OF THE INVENTION

The indiscriminate use of fertilisers has produced the presence of high concentrations of nitrates, nitrites, phosphates and other nutrients in ground waters and springs, with the resulting risk for human and animal health, as well as for adequate preservation of the environment. This fact has caused the appearance of new laws, aimed at controlling the maximum amount of fertilising units that farmers may use per crop cycle, according to the degree of contamination present in their work area (De Clercq, P., et al. Nutrient Management Legislation in European Countries. Wagenigen Pers. Holland. 2001).
A possible solution to these problems is the use of slow-release fertilisers coated with water-insoluble membranes which slow down nutrient release according to soil moisture and temperature (Thompson et al. US 5,089,041, 1992; Zlotnikov et al. US 5,454,851, 1995). Although these products allow significantly reducing washout, volatilisation, or retrogradation losses, are not well adapted to nourishing short cycle or annual crops because the nutrient release dynamics are not suitably adapted to the dynamics associated to the crop necessities (Jiménez Gómez, S. Fertilizantes de Liberación lenta (Slow-release Fertilisers). 1992. Mundi Prensa, Madrid; p. 1).
In the case of nitrogen, nitrification and urease inhibitors have been proposed which slow down the transformation of ammonium and ureic nitrogen, respectively, in soils.
The problem with these products is that they do not control water solubility - and therefore the immediate presence of the products in the soil solution - but the nitrogen forms present in soils (ureic, ammonium or nitric forms). For this reason, although volatilisation phenomena may be controlled, other phenomena such as leaching are not controlled (Engelstad, O.P. Fertilizer Technology and Use. 1985. SSSA, Madison).
Still with regard to nitrogen, different urea polymers have been proposed, the release or assimilability of which depends on the activity of soil microorganisms. These products have been proven effective in gardening and in decorative plants, but not in industrial or intensive crops (Engelstad, O.P. Fertilizer Technology and Use. 1985. SSSA, Madison).
With regard to phosphorus (P) and binary forms P(N) or P(K), products such as natural phosphate and double phosphates of Mg and ammonium (Vilain et al. 1932. GB 377,720; Urbain, E. 1932. GB 379,434) or K(Na) and Mg(Ca) (Kerschbaum, F. 1937. GB 475,993; Franz, S. 1954. GB 704,115;), or Al(Ca) (called Phospal), have been proposed. These products are insoluble in water and may be assimilable as they are soluble in citric or formic acid under heat. However, when the solubility of these compounds in neutral ammonium citrate is studied - accepting solubility to neutral ammonium citrate as a measure of the potential degree of assimilability of a fertiliser - it is observed that their solubility is very low, therefore the potential degree of assimilability of these compounds for plants is actually low (Morel and Fardeau. Agronomical evaluation of phosphate fertilizer as a nutrient source of phosphorous for crops: isotopic procedure. Fertilizer Research 24, 115-122. 1990). In fact the K(Mg) and K(Ca) double phosphates form ceramic materials are used for isolating hazardous materials such as radioactive materials (Baldwin, Ch. et al. 1999. WO9942382).
The foregoing is consistent with the results obtained in different studies which have shown the relative inefficiency of these compounds to provide really assimilable nutrients for the plants (Morel and Fardeau. Agronomical evaluation of phosphate fertilizer as a nutrient source of phosphorous for crops: isotopic procedure. Fertilizer Research 24, 115-122. 1990).
A patent for a slow-release potassium divalent metal phosphate product has also been proposed (Moore, W. 1994. US 5,374,294), by means of reacting phosphoric acid, potassium hydroxide and a divalent metal oxide. The problem with this product is that it presents cold water solubility between 35 and 98%, due to which the washout control is very low.
In this context, the development of more efficient fertilisers that allow making adequate crop nutrition compatible with the maximum reduction of losses by washout as well as by volatilisation and retrogradation, has unquestionable interest.
The object of the present invention constitutes a solution to the problem of compatibility of nutrient loss control and adequate nutrition of annual cycle plants.

BRIEF DESCRIPTION OF THE INVENTION

In one aspect the invention is related to a fertilising composition comprising an inorganic matrix insoluble in water but soluble in the organic acids released by the plant roots into the rhizosphere.
Another aspect of the invention is a method for preparing the fertilising composition.
A further aspect of the invention is a method for soil fertilisation that allows making adequate crop nutrition compatible with the maximum reduction of fertiliser losses.

DESCRIPTION OF THE DRAWINGS

Figure 1 shows the effect of the RCF components and the traditional fertiliser (F) on the chlorophyll content SPAD index, ear number and grain number.
Figure 2 shows the effect of the RCF compositions and traditional fertiliser (F) on leached nitrogen percentage expressed as a percentage with respect to the control (F).
Figure 3 shows the effect of the RCF formulation manufactured according to Example 2 on the degree of losses by volatilisation.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a fertilising composition comprising an inorganic matrix insoluble in water but soluble in the organic acids released by the plant roots into the rhizosphere.
An important feature of this invention is that the progressive solubility of the product is controlled by the plant by means of the molecular signals that it emits to the rhizosphere in response to the nutrient needs.
These signals are summarised in (Pinton et al. The Rhizosphere. Marcel Dekker. 2001):

Low molecular weight organic acids with high complexing ability.
pH acidification
Multiplication of microbiota activity

The fertilising composition of the invention therefore comprises an inorganic matrix insoluble in water but soluble in the organic acids released by the plant roots into the rhizosphere, wherein said matrix comprises one or several double phosphorus salts with calcium or magnesium, and one of the metals chosen from Fe, Al, Mn, Cu, Zn, B and Co, with the condition that Al is chosen only when the other double salt element is Mg.
In a preferred embodiment, the fertilising composition of the invention further comprises an initiating fraction, made up of water soluble salts of one or several elements chosen from Ca, Mg, Fe, Al, Mn, Cu, Zn, B and Co. The water soluble salts can be, for example, simple sulphates and/or phosphates of one or several elements chosen from Ca, Mg, Fe, Al, Mn, Cu, Zn, B and Co.
In a particular embodiment, the double salts forming part of the matrix insoluble in water but soluble in the organic acids released by the plant roots into the rhizosphere are optionally chemically associated to organic compounds with chelating ability by means of metal bridges.
The organic compounds with chelating ability are preferably chosen from the group formed by humic acids, fulvic acids, lignin, lignosulphonates, synthetic chelating agents, low molecular weight carboxylic acids and mixtures thereof, as well as organic substrates containing compounds with chelating ability such as peat, compost, fresh plant residues.
In a particular embodiment, the low molecular weight carboxylic acids are chosen from citric acid and oxalic acid and the phytoregulators and pesticides are chosen from the group formed by those of natural origin and those which are synthetic.
In another particular embodiment the synthetic chelating agent is EDTA.
In a preferred embodiment the chelating agent is humic acid.
In a preferred embodiment, the fertilising composition further comprises one or several nutrients chosen from nitrogen and potassium sources and sources of organic matter, nitrification or urea hydrolysis inhibitors, phytoregulators and pesticides, which are integrated or encapsulated in the water insoluble matrix and the release of which is associated to the release of the elements of the matrix.
Preferably, the phytoregulators are chosen from the group formed by cytokinins, gibberellins, salicylates, polyamines and brassinosteroids, and the pesticide is chosen from the group formed by nematicides, insecticides and bactericides. These can be of natural origin (for example, marine algae extracts, plant material compost, etc.) or synthesised.
The pesticides may be chosen from one or more fungicides, nematicides, insecticides, bactericides, etc., both of natural origin (for example, plant extracts, essential oils, etc.) or synthesised.
According to a particular embodiment the potassium source is a potassium salt and the nitrogen source is ammonium, nitrate, urea or an organic nitrogen source different to urea, such as heterocyclic compounds, proteins, peptides or urea polymers, such as urea formaldehyde.
More preferably, the potassium salt is potassium chloride.
According to a particular embodiment the fertilising composition contains double salts of phosphorus, calcium, iron and/or phosphorus, calcium, zinc.
According to another particular embodiment the fertilising composition contains two double salts, one of phosphorus, magnesium and iron and another one of phosphorus, magnesium and zinc.
The fertilising compositions may be presented in powder, granulated, pellet or compacted form.
In the fertilising formulation object of the invention two complementary fractions may then be integrated:

Initiating fraction made up of the water soluble nutrient fraction which allows beginning the functional activity of the root and of the plant itself. This fraction can normally form between 10% and 30% of the total.
Stable fraction called RCF (Rhizosphere-Controlled Fertiliser) made up of by the matrix of the water insoluble nutrient fraction but which is gradually made soluble by the action of the organic acids released by the plant roots into the rhizosphere.

As the inorganic matrix becomes soluble, the release of the rest of the nutrients optionally integrated therein is also allowed.
Another aspect of the invention consists in a preparation method for preparing a fertilising composition comprising a matrix insoluble in water but soluble in the organic acids released by the plant roots into the rhizosphere.
The preparation method comprises the step of preparing an inorganic matrix insoluble in water but soluble in the organic acids released by the plant roots into the rhizosphere, simultaneously reacting:

a. One or several acids chosen from phosphoric acid, phosphorous acid, pyrophosphoric acid, polyphosphoric acid, sulphuric acid and mixtures thereof,
b. One or several Ca and/or Mg compounds chosen from oxide, hydroxide, carbonate, phosphate, silicate, sulphate, chloride and nitrate.
c. One or several compounds containing one or several of the following elements: Fe, Al (only when the other element of the salt is Mg), Cu, Mn, Zn, B and Co, chosen from oxide, hydroxide, carbonate, phosphate, silicate, sulphate, chloride and nitrate.

In a particular preparation method, sulphuric acid is used as the only attacking acid and phosphates are used as Ca or Mg and P sources.
In a preferred method, the phosphoric, phosphorous, pyrophosphoric, polyphosphoric, sulphuric acids or mixtures thereof are optionally mixed, either previously or in the reaction medium, with organic substances or compounds with complexing or chelating ability.
In a particular embodiment, the organic substances or compounds with complexing or chelating ability are chosen from the group of humic acids; fulvic acids; organic materials containing compounds with chelating ability such as peat, compost, fresh plant residues; lignin; lignosulphates; synthetic chelating agents such as EDTA and low molecular weight carboxylic acids such as citric acid or oxalic acid.
Organophosphates are thus obtained, in which the organic compound with chelating ability is chemically associated with the phosphorus nucleus by means of bridges formed by the metal.
In the preparation method of the invention the granulometry of the solid components is not a determining factor, but is preferably under 200 microns.
In a preferred embodiment, water soluble salts of one or several of the elements chosen from Ca, Mg, Al, Mn, Cu, Zn, B and Co are formed as reaction byproducts, forming the initiating fraction comprised in the fertilising composition. The soluble salts may be, for example, simple phosphates and/or sulphates of one or several of the elements chosen from Ca, Mg, Fe, Al, Mn, Cu, Zn, B and Co.
The water soluble salts can be formed in variable proportions, depending on the reaction conditions, particularly on the proportion between the acids used and the compounds providing the elements Ca, Mg, Fe, Al, Mn, Cu, Zn, B and Co. Therefore, according to a particular embodiment of the fertilising composition preparation method the ratio of acids:compounds containing Ca, Mg, Fe, Al, Mn, Cu, Zn, B and Co is greater than the stoichiometric ratio.
According to another particular manner of carrying out the preparation method, the ratio of acids:compounds containing Ca, Mg, Fe, Al, Mn, Cu, Zn, B and Co is less than the stoichiometric ratio.
In another preferred embodiment, one or several components chosen from: nitrogen and potassium sources, organic matter sources, nitrification or urea hydrolysis inhibitors, phytoregulators and/or pesticides are additionally introduced in the inorganic matrix insoluble in water but soluble in the organic acids released by the plant roots into the rhizosphere. These optional fertilising composition components can be incorporated during the preparation process by means of mixing and granulating these substances with the previously obtained matrix.
The reaction for obtaining the inorganic matrix insoluble in water but soluble in the organic acids released by the plant roots into the rhizosphere can be performed in any type of mixer-reactor that allows mixing liquid and solid components, for example, a Lodige mixer, a blade or helix mixer, Kuhlman reactor, etc.
The temperature at which the liquid components are added is not a determining factor, but it is preferably between 20°C and 50°C.
The process can be performed in a continuous or discontinuous manner, the optimal reaction time being 15 minutes.
The reaction can be carried out:

1. Simultaneously adding the different components to the reactor.
2. Premixing - which may include grinding - the solid components, after mixing - reacting with the liquid components.
3. The liquid components may be premixed with the solid components before the reaction.

Working temperature and pressure are not determining factors, therefore, it is possible to conduct the reaction at room temperature and atmospheric pressure, which forms a practical advantage of this process.
The optional incorporation of other nutrients, such as nitrogen and potassium sources, organic matter sources, nitrification or urea hydrolysis inhibitors, phytoregulators and/or pesticides, to the fertilising composition is carried out by mixing the different matters and granulation, either by means of the technique of granulating drum in solid-liquid phase and subsequent drying, or by extrusion or compaction.
Another aspect of the invention is formed by a soil fertilisation method which allows making adequate crop nutrition compatible with the maximum reduction of fertilisation losses, comprising applying a composition of the invention to the soil.
Included below are non-limiting examples of some embodiments of the invention.

Example 1

Obtaining a matrix comprising a mixture of double salts of P (Mg)(Fe) and P(Mg)(Zn)

To obtain approximately 1.5 kg of a mixture of double salts of P(Mg)(Fe) and P(Mg)(Zn) according to the present invention, the following was carried out.

1. 989.4 g of phosphoric acid (68%) are reacted with 500 g of magnesium oxide, 103.7 g of iron carbonate and 96 g of zinc carbonate by means of mixing.
The reaction is carried out by means of simultaneous mixing of the components in a Kuhlman-type reactor. The product is set in 15 minutes.
The solid products have been previously ground until 90% are under 100 µm.
2. The product is left to cure for 24 h.

The typical analysis of the obtained product is shown in Table 1.

Table 1. Typical analysis of a basic RCF product, obtained by means of reacting phosphoric acid with Mg oxides and Zn and Fe carbonates.

Parameters (%)	RCF
Fe - Total (as Fe)	3.1
Fe - citrate (as Fe)	1.6
Fe - water (as Fe)	0.002
P - total (as P₂O₅)	34.5
P - citrate (as P₂O₅)	34
P - water (as P₂O₅)	14
Mg - total (as MgO)	24.2
Mg - citrate (as MgO)	24.2
Mg - water (as MgO)	3.7
Zn - total	3.8
Zn - citrate (as Zn)	3.7
Zn - water (as Zn)	0.02

Water: soluble in water
Citrate: soluble in neutral ammonium citrate
Total: soluble in concentrated hydrochloric acid.

Solubility in neutral ammonium citrate is taken as a measurement of the fertiliser solubility in the organic acids released by the plant roots into the rhizosphere and therefore as an indicator of their potential degree of assimilability.

Example 2

Obtaining a complete fertiliser from a matrix comprising a mixture of double salts of P(Mg)(Fe) and P(Mg)(Zn)

1. The following are mixed in a Lodige mixer:
- 312.5 g of the matrix comprising a mixture of double salts of P(Mg)(Fe) and P(Mg)(Zn) obtained in Example 1.
- 200 g of potassium chloride
- 119 g of ammonium sulphate
- 10.87 g of urea
- 26.51 g of melamine
- 15 g of grape marc compost
- 25 g of soluble solid extract of a marine algae of the ascophyllum family
- 0.1 g of benzylaminopurine
- 0.01 g Folpet
- 150 g of water vapour
The solid products have been previously ground until 90% are under 100 µm.
2. The product from 1 is granulated in a granulating drum by adding water vapour
3. The product from 2 is dried in a drying drum using counterflow hot air at 300°C.

A typical mineral analysis of the product obtained from Example 2 is shown in Table 2.

Table 2

Parameters	Units	Values
Ph	-	6.9
Electric conductivity	mS/cm
Moisture	%	1.1

Macroelements
N - total (Dumas)	%	27.3
N - ammonium	%	3.7
P - total (as P₂O₅)	%	10
P - citrate (as P₂O₅)	%	9.3
P - water (as P₂O₅)	%	5.6
Mg - total (as MgO)	%	7.1
Mg - citrate (as MgO)	%	6.6
Mg - water (as MgO)	%	2.2
Sodium (as Na)	%

Trace Elements
Iron - total	%	0.85
Iron - citrate	%	0.3
Iron - water	%		0
Zinc - total	%	1.1
Zinc - citrate	%	1.1
Zinc - water	%	0.028
K - total (as K₂O)	%	11.8
K - citrate (as K₂O)	%	11.7
K - water (as K₂O)	%	10.9

Water: soluble in water
Citrate: soluble in neutral ammonium citrate
Total: soluble in concentrated hydrochloric acid
Iron and zinc are expressed as iron and as zinc.

Example 3

Obtaining a matrix comprising a mixture of double salts of P(Mg)(Fe)(humic acid) and P(Mg)(Zn)(humic acid)

To obtain 1.5 kg of the matrix comprising a mixture of double salts of P(Mg)(Fe)(humic acid) and P(Mg)(Zn)(humic acid) according to the invention, the following was carried out.

1. 989.4 g of phosphoric acid (68%) and 200 g of a humic acid previously mixed with stirring are reacted with 500 g of magnesium oxide, 103.7 g of iron carbonate and 96 g of zinc carbonate by means of mixing.
The reaction is carried out by means of simultaneous mixing of the components in a Kuhlman-type reactor. The product is set in 15 minutes.
The solid products have been previously ground until 90% are under 100 µm.
2. The product is left to cure for 24 h.

Example 4

Obtaining a matrix comprising a mixture of double salts of P(Mg)(Fe) and P(Mg)(Zn)

To obtain about 1.5 kg of a compound a matrix comprising a mixture of double salts of P(Mg)(Fe) and P(Mg)(Zn) according to the invention, the following was carried out.

1. 1,000 g of phosphorous acid (68%) are reacted with 500 g of magnesium oxide, 103.7 g of iron carbonate and 96 g of zinc carbonate by means of mixing.
The reaction is carried out by means of simultaneous mixing of the components in a Kuhlman-type reactor. The product is set in 15 minutes.
The solid products have been previously ground until 90% are under 100 µm.
2. The product is left to cure for 24 h.

Example 5

To obtain about 1.5 kg of a matrix comprising a mixture of double salts of P(Mg)(Fe) and P(Mg)(Zn) according to the invention, the following was carried out.

1. 989.4 g of phosphoric acid (68%) are reacted mixing with 700 g of magnesium carbonate, 90 g of iron sulphate and 90 g of zinc oxide by means of mixing.
The reaction is carried out by means of simultaneous mixing of the components in a Kuhlman-type reactor. The product is set in 15 minutes.
The solid products have been previously ground until 90% are under 100 µm.
2. The product is left to cure for 24 h.

Example 6

Obtaining a matrix comprising a double salt of P(Ca)(Fe)

To obtain about 2.8 kg of a matrix comprising a double salt of P(Ca)(Fe) according to the invention, the following was carried out.

1. 1,000 g of sulphuric acid (70%) are reacted with 1200 g of phosphoric rock (apatite tricalcium phosphate of 32% P₂O₅), 1000 g of iron sulphate heptahydrate (24% total Fe) by means of mixing.
The reaction is carried out by means of simultaneous mixing of the components in a Kuhlman-type reactor. The product is set in 15 minutes.
The solid products have been previously ground until 90% are under 100 µm.
2. The product is left to cure for 24 h.

Example 7

Obtaining a matrix comprising a mixture of double salts of P(Ca)(Fe) and P(Ca)(Zn)

To obtain about 2.5 kg of a matrix comprising a mixture of double salts of P(Ca)(Fe) and P(Ca)(Zn) according to the invention, the following was carried out.

1. 1300 g of phosphoric acid (68%) are reacted with 1000 g of phosphoric rock (apatite tricalcium phosphate of 32% P₂O₅) and 800 g of iron sulphate heptahydrate and 300 g of zinc oxide by means of mixing. The reaction is carried out by means of simultaneous mixing of the components in a Kuhlman-type reactor. The product is set in 15 minutes.
The solid products have been previously ground until 90% are under 100 µm.
2. The product is left to cure for 24 h.

Example 8

Obtaining a matrix comprising a double salt of P(Ca)(Fe)(humic acid)

To obtain about 2.8 kg of a matrix comprising a double salt of P(Ca)(Fe)(humic acid) according to the invention, the following was carried out.

1. 600 g of sulphuric acid (70%), 300 g of phosphoric acid (68%) and 200 g of humic acid (25%) are reacted with 1200 g of phosphoric rock (apatite tricalcium phosphate of 32% P₂O₅), 1,000 g of iron sulphate heptahydrate (24% total Fe).
The reaction is carried out by means of simultaneous mixing of the components in a Kuhlman-type reactor. The product is set in 15 minutes.
The solid products have been previously ground until 90% are under 100 µm.

Examples of the global effect of the formulations object of the invention

Example 9

Comparative study of the solubility of phosphorus at 22°C over time in neutral ammonium citrate (NAC), of a composition object of the invention according to Example 1 and the phosphal fertiliser (calcined calcium aluminium phosphate)

Solubility was obtained by means of stirring 1 g of product in 100 ml of neutral ammonium citrate at a temperature of 22°C, and measurement was carried out every 15 minutes.

The results are shown in the following table (Table 3).

Table 3

Time/produc. Minutes	Phosphal (NAC) % solubilised P	RCF (NAC) % solubilised P
15	0.01	85
30	0.05	90
45	0.1	100
60	0.1	100
75	0.1	100
90	0.1	100
105	0.1	100
120	0.1	100
135	0.1	100
150	0.1	100

Example 10

Effect of the RCF composition obtained in the composition from Example 2 on the development of wheat plants grown in limestone soil, nitrogen losses by leaching and nitrogen losses by volatilisation

This study was carried out in the R&D Department of Inabonos SA (San Francisco, S., Urrutia, O., Casanova, E., Zamarreño. A. M^a and García-Mina, J. M^a. 2003)

Methodology

Short cycle wheat seeds (Farak) grown in 6.6 litre pots with perforated bases were used to determine also the leaching with respect to irrigation. Once germinated, 7 seedlings were left in each pot for the purpose of reproducing the usual sowing density (450 seeds per m²).
The soil used came from Iza (Navarra) and was mixed with 50% siliceous sand to facilitate draining.
The basic chemical analysis of the soil was: pH 8.08, EC 0.66 mS cm², OM 0.66% and carbonate content was 53.84%. P content was also very low (9.47 ppm), as well as the assimilable micronutrient content: 6.6 ppm Fe; 0.57 ppm Cu; 7 ppm Zn and 0.43 ppm Mn.
The following treatments were used:

Control 0: did not receive fertilisation.
Control F: consisting in the traditional fertilisation on the surface at tillage corresponding to 350 kg/Ha of 8-15-15 and 330 kg/Ha of urea to the (180 nitrogen units; 52.5 P₂O₅ units; 52.5 K₂O units) (harvest predicted between 5,000 and 6,000 kg/Ha).
RCF 1: consisting in the deep application at seeding of 650 kg/Ha of 18-9-12 MgO Oligo RCF (117 nitrogen units; 58.5 P₂O₅ units; 78 K₂O units).
RCF 2: consisting in the deep application at seeding of 830 kg/Ha of 18-9-12 MgO Oligo RCF (149 nitrogen units; 74.7 P₂O₅ units; 99.6 K₂O units).
RCF 3: consisting in the deep application at seeding of 1.000 kg/Ha of 18-9-12 MgO Oligo RCF (180 nitrogen units; 90 P₂O₅ units; 120 K₂O units).

The expression MgO Oligo means that the fertiliser also contains 2% Mg and 0.1% Fe and Zn.
RCF means that the fertiliser corresponds to the fertilisers of this invention (rhizosphere-controlled fertiliser).
If the necessity of 23 kg of N per ton of grain is considered, the extraction of a production of 5,500 kg/Ha would be of 126 kg N/Ha.
Thus, unit quantities with the RCF 1 treatment are obtained which correspond to those extracted by the crop, and which correspond to 35% less nitrogenous units compared to the control treatment corresponding to the traditional fertiliser. However with the RCF 2 and RCF 3 treatments a 27% reduction in nitrogen units and the same nitrogenous fertilisation with respect to the control containing the traditional fertiliser would be obtained.
The products were manufactured as described in Example 2.
The leaching was collected weekly corresponding with irrigation. Nitrogen content and forms in the leaching were evaluated.
Two harvests were performed, one after 30 days and another one after 60 days at the beginning of grain maturation.
The dry weight of root and aerial part, ear number and grain number - all expressed by pot - as well as the mineral nutrient content, were evaluated.

Results

The results are shown in Figures 1-3.
From Figure 1, which shows the effect of the RCF compositions and the traditional fertiliser (F) on the SPAD index relative to the chlorophyll content, on ear number and on grain number, it can be observed that the RCF treatments showed higher results than the control (F), even with the reduction of nitrogen units.
According to Figure 2, which illustrates the effect of the RCF compositions and the fertiliser (F) on the percentage of leached nitrogen expressed as a percentage compared to the control (F), it is deduced that the RCF treatments were associated to a significant reduction of nitrogen leaching and, therefore, of the potential degree of contamination.
As can be observed in Figure 3, referring to the effect of the RCF composition manufactured according to Example 2 on the degree of losses by volatilisation, the RCF composition allows significantly reducing losses by ammonium volatilisation.

Claims

A fertilising composition, comprising an inorganic matrix insoluble in water but soluble in the organic acids released by the plant roots into the rhizosphere, wherein said matrix comprises one or several double salts of phosphorus with calcium or magnesium, and one of the metals chosen from Fe, Al, Mn, Cu, Zn, B and Co, with the condition that Al is chosen only when the other element of the double salt is Mg.
A composition according to claim 1, characterised in that it further comprises an initiating fraction formed by water soluble salts of one or several of the elements chosen from Ca, Mg, Fe, Al, Mn, Cu, Zn, B and Co.
A composition according to claim 2, characterised in that the water soluble salts are simple sulphates and/or phosphates of one or several of the elements chosen from Ca, Mg, Fe, Al, Mn, Cu, Zn, B and Co.
A fertilising composition according to claims 1, 2 and 3, characterised in that it further comprises other nutrients chosen from nitrogen and potassium sources, organic matter sources, nitrification or urea hydrolysis inhibitors, phytoregulators and pesticides, which are integrated or encapsulated in the water insoluble matrix and the release of which is associated to the release of the elements of the matrix.
A fertilising composition according to claim 1, characterised in that the double salts are chemically associated to organic compounds with chelating ability by means of metal bridges.
A fertilising composition according to claim 5, characterised in that the organic compounds with chelating ability are chosen from the group formed by humic acids, fulvic acids, lignin, lignosulphonates, synthesis chelating agents, low molecular weight carboxylic acids and mixtures thereof, as well as organic substrates containing compounds with chelating ability such as peat, compost, fresh plant residues.
A composition according to claim 6, characterised in that the low molecular weight carboxylic acids are chosen from citric acid and oxalic acid, and the phytoregulators and pesticides are chosen from the group formed by those of natural origin and those which are synthetic.
A fertilising composition according to claim 6, characterised in that the synthesis chelating agent is EDTA.
A fertilising composition according to claim 6, characterised in that the chelating agent is a humic acid.
A composition according to claim 4, characterised in that the phytoregulators are chosen from the group formed by cytokinins, gibberellins, salicylates, polyamines and brassinosteroids, and the pesticide is chosen from the group formed by nematicides, insecticides and bactericides.
A fertilising composition according to claim 4, characterised in that the potassium source is a potassium salt and the nitrogen source is ammonium, nitrate, urea or an organic nitrogen source different to urea, such as heterocyclic compounds, proteins, peptides or urea polymers, such as urea formaldehyde.
A fertilising composition according to claim 11, characterised in that the potassium salt is potassium chloride.
A fertilising composition according to claims 1 to 12, characterised in that the double salts are of phosphorus, calcium, Fe and/or phosphorus, calcium, Zn.
A fertilising composition according to claims 1 to 12, characterised in that it contains two double salts. One of phosphorus, magnesium and Fe; and another of phosphorus, magnesium and Zn.
A fertilising composition according to previous claims, characterised in that it is presented in powder, granulated, pellet or compacted form.
A method for preparing a fertilising composition according to claim 1, comprising preparing an inorganic matrix insoluble in water but soluble in the organic acids released by the plant roots into the rhizosphere, simultaneously reacting:
a. one or several acids chosen from phosphoric acid, phosphorous acid, pyrophosphoric acid, polyphosphoric acid, sulphuric acid and mixtures thereof,

b. one or several Ca and/or Mg compounds chosen from oxide, hydroxide, carbonate, phosphate, silicate, sulphate, chloride and nitrate.

c. one or several compounds containing one or several of the following elements: Fe, Al (only when the other element of the salt is Mg), Cu, Mn, Zn, B and Co, chosen from oxide, hydroxide, carbonate, phosphate, silicate, sulphate, chloride and nitrate.
The method of claim 16, characterised in that the ratio of acids:compounds containing Ca, Mg, Fe, Al, Mn, Cu, Zn, B and Co is greater than the stoichiometric ratio.
The method of claim 16, characterised in that the ratio of acids:compounds containing Ca, Mg, Fe, Al, Mn, Cu, Zn, B and Co is less than the stoichiometric ratio.
A method according to claims 16 to 18, characterised in that sulphuric acid is used as the only acid, and phosphates are used as Ca and/or Mg compounds.
A method according to claims 16 to 18, characterised in that the phosphoric, phosphorous, pyrophosphoric, polyphosphoric, sulphuric acids or mixtures thereof are mixed either previously or in the reaction medium with organic substances or compounds with complexing or chelating ability.
A method according to claim 20, characterised in that the substances or compounds with chelating ability are chosen from the group of humic acids, fulvic acids, organic materials containing compounds with chelating ability such as, for example, peat, compost, fresh plant residues; lignin, lignosulphates, synthesis chelating agents such as EDTA and low molecular weight carboxylic acids such as citric or oxalic acids.
A method according to claims 16 to 21, characterised in that when the reacting substances are found in solid state, their granulometry is under 200 microns.
A method according to claims 16 to 22, characterised in that water soluble salts of one or several of the elements chosen from Ca, Mg, Fe, Al, Mn, Cu, Zn, B and Co, forming the initiating fraction comprised in the fertilising composition, are formed as reaction byproducts, .
A method according to claim 23, characterised in that the water soluble salts are simple sulphates and/or phosphates of one or several of the elements chosen from Ca, Mg, Fe, Al, Mn, Cu, Zn, B and Co.
A method according to claims 16 to 24, characterised in that one or several of the components chosen from nitrogen and potassium sources, organic matter sources, nitrification or urea hydrolysis inhibitors and/or pesticides are introduced in the inorganic matrix insoluble in water but soluble in the organic acids released by the plant roots into the rhizosphere.
A method according to claim 25, characterised in that the introduction of the components chosen from nitrogen and potassium sources, organic matter sources, nitrification or urea hydrolysis inhibitors and pesticides is carried out by means of mixing (prior claim 24).
A method for fertilising soil which allows making adequate crop nutrition compatible with the maximum reduction of fertiliser losses, comprising the application to the soil of a composition according claims 1 to 15.